Many piping systems require periodic or emergency repairs and maintenance of in-line devices. Examples of such in-line devices are valves, filters, flow controls, and sensors. These are merely exemplary of many other types of piping system components. Usually these are fixed to some substrate structure, or perhaps are partly or entirely encased or buried. In order to connect to these components, a union must be provided whose length can be reduced for access purposes, and enlarged for connection purposes. Such unions are useful both for procedures conducted after installation, and also for procedures conducted as part of an original installation.
Unions for these purposes are well-known. They often are referred to as "slip" or "telescopic" joints. They share the required function of enabling a pair of tubes to telescope relative to one another with a sliding seal between them. Attachment means as provided at both ends so the device can structurally be incorporated into a piping system. The union of this invention also provides these properties.
In the prior art devices, there has always been the nagging problem that shortening and lengthening the union are equally convenient, and that it was possible readily to separate the two tubes. Is is clearly preferably to facilitate the shortening of the device for installation purposes, but desirable to make it relatively more difficult to separate the tubes or to disassemble the tubes from each other, in order to make a better fluid sealing joint, and in order to keep the union in one piece during handling.
It is an object of this invention to provide a union which can readily be reduced in length, less readily be elongated, and less readily be disassembled, all compared to unions in which reduction or enlargement of length are equally conveniently attained, and in which the two tubes are readily separated.